You need the Kekkei Genkai infobox and an SVG file icon that is appropriately named for the system to recognize as the symbol of that KG to be used in character infoboxes.
Example: Wood Release is an elemental KG that uses the KG infobox and has the "Nature Icon Wood.svg" file uploaded for it. The same is utilized for any other KG, where the SVG file must be named after the KG itself. The Rinnegan utilizes the "Rinnegan.svg." file for it's symbol.
Again though, it MUST be an SVG file created using scale vector graphics. If it's done the cheap method of making a PNG and then copy+pasting it into a vector graphic manipulation program like Inkscape or Adobe Illustrator, then the scaling of the symbol will be pixelated. Scale Vector Graphics work very differently than standard picture file formats.